Methods and compositions for dielectric materials

ABSTRACT

The present invention comprises methods and compositions of dielectric materials. The dielectric materials of the present invention comprise materials having a dielectric constant of more than 1.0 and less than 1.9 and/or a dissipation factor of less than 0.0009. Other characteristics include the ability to withstand a wide range of temperatures, from both high temperatures of approximately +260° C. to low temperatures of approximately −200° C., operate in wide range of atmospheric conditions and pressures (e.g., a high atmosphere, low vacuum condition such as that found in the outer-space as well as conditions similar to those found at sea level or below sea level). The dielectric materials of the present invention may be used in the manufacture of composite structures that can be used alone or in combination with other materials, and can be used in electronic components or devices such as RF interconnects.

RELATED APPLICATIONS

This application is a continuation in part of and claims the benefit ofU.S. patent application Ser. No. 11/334,947, filed Jan. 19, 2006, whichclaims the benefit of U.S. Provisional Patent Application No.60/644,976, and a continuation in part of PCT Application No.PCT/US2006/002012, filed Jan. 19, 2006. All of them are hereinincorporated by reference in their entirety.

FIELD OF INVENTION

The present invention is directed to dielectric materials and methods ofmaking and using such materials, particularly in laminate articles andassemblies comprising at least one dielectric material for circuitboards, insulators, radar microwave, RF interconnects, and otherapplications.

BACKGROUND OF THE INVENTION

Composite or laminate structures are the basis for many applications inthe electronics industry. Advances in printed wiring board laminateshave lead to faster, smaller, lighter and cost effective electroniccomponents for use in applications such as radar, antennas, telephony,computer board components, wireless and cellular technology, RFinterconnects, and microwave devices. The characteristics of thematerials used to make the composites affect the technical abilities andapplications for which the composite or laminate structure can be used.

A variety of composite structures are used in the electronics industry.Technical requirements for such composites include the structuralintegrity of the finished structure, the ability of the individualcomponents to withstand the rigors of assembly, the ability of theassembled structure to withstand a variety of processing conditions,such as those used in making printed wired circuit board (including,e.g., the ability to withstand high temperature conditions asexperienced during soldering operations and the ability to interconnectlayers by means of plating through vias), the performance properties ofthe components used and the finished structure (including the dielectricconstant, resistance to environmental conditions such as moisture,atmosphere, harsh chemicals, and heat), costs of the components, andcosts associated with the manufacture of the finished article.

One component of a laminate is the dielectric material that is used. Adielectric material is an insulating material that does not conductelectrons easily and thus has the ability to store electrical energywhen a potential difference exists across it. The stored energy is knownas an electric potential or an electrostatic field which holdselectrons. The electrons are discharged when the buildup of electrons issufficiently large. Common dielectric materials include glass, mica,mineral oil, paper, paraffin, polystyrene, plastics, phenolics, epoxies,aramids, and porcelain. The characteristics of the dielectric aredetermined by the material from which it is made and its thickness.

In electronic circuits, dielectric materials may be employed incapacitors and as circuit board substrates. Conventionally, dielectricconstant materials are used in radar or microwave applications and alsofor circuit miniaturization as the speed of propagation of signal at aconstant frequency is proportional to the inverse of the square root ofthe dielectric constant of the medium through which it passes. Lowdielectric constant materials are used for high speed, low losstransmission of signals as such materials allow faster signalpropagation, and less space is required in circuitry design or inconductive layers. Low dielectric materials also have radar andmicrowave applications. If the combination of materials is such that theloss tangent for a material of a given frequency signal is very low, thecircuit board will allow very efficient transmission or splitting of thesignal without electrical loss related to the hysteresis loop. If awhole circuit were built on low dielectric material, one could amplifythe signal only a certain amount at each mounted transistor, and becauseof the lower power involved, the assembly would reduce the build up ofexcessive heat and temperature. Consequently, the amplification would bespread over a large space. If all of the dielectric material had a highdielectric constant, there would be more loss at signal splits so thatmore transistors would be necessary to maintain a specific signal tonoise ratio, and more power would be required to operate thesecomponents.

One of the common materials used in the production of printed circuitboards, which are used in antennas and other elements of cellular andwireless technology, is glass fiber and/or woven glass materials thatare coated with PTFE (polytetrafluoroethylene), cyanate ester, Aramids,and/or PTFE films. These materials have been used because they can bemanufactured readily. However, they are more expensive than many otherhigher dielectric printed circuit materials, and require multiple stepsto manufacture. They are also relatively heavy due to its density ofabout 2.5 gm/cm³. Furthermore, these materials generally have adielectric constant no lower than about 2.17.

Efforts have been made to provide materials that are lighter and havelower dielectric constants. Such efforts include making a structure inwhich a microballoon-filled adhesive is used to bond metal foil directlyto a rigid polyisocyanurate foam. While potentially useful inmanufacturing individual antennas, the method is limited in that thereis no true barrier to attack of the foam surface by process chemistries(both aqueous and organic) typical of printed wiring board manufacturingprocesses once the copper has been etched away. This results indegradation of and/or inconsistency in electrical properties andperformance. Another known weakness with the polyisocyanurate foam isdegradation when exposed to ultraviolet rays. Thus, this method cannotbe used in the high volume continuous manufacturing necessary to producea product economically.

Other problems also arise during the manufacturing process. For example,scientists have attempted to resolve the issue of degraded electricalperformance by using a polyurethane film adhesive to bond copper foildirectly to a rigid Baltek polystyrene foam core at 350° F. However,such treatment led to the partial structural collapse of the foam anddid not result in an impermeable barrier between the copper and thefoam. The resultant product had pinholes in the film/bonding layer,which resulted in the penetration of etch chemicals during processing.Another attempt was to coat the foam itself with a ceramic-filled resinsystem known to have good electrical properties. Again the foamcollapsed due to heat and pressure, resulting in a material that was toodense and the seal between the copper and the foam was still inadequateto eliminate etchant penetration and entrapment in the foam structure.Other composites also have been investigated, such as polyethylene inclosed and open cell forms. The results indicate that the materialstructure and integrity of the product was compromised in these studies.Many of these polyethylene and polystyrene foam materials also cannotsurvive processing required to plate connecting holes.

There is a need for a dielectric material that has at least one of thedesirable characteristics, such as, a low dielectric constant, a lowloss tangent, the ability to withstand a wide range of temperatures, theability to operate in wide range of atmospheric conditions andpressures, and capable of being used in the manufacture of compositestructures that can be used alone or in combination with othermaterials. Such completed assemblies could form electronic componentsused in electronic devices.

SUMMARY OF THE INVENTION

The present invention comprises methods and compositions for dielectricmaterials that are useful in laminate structures, components, orassemblies of multiple components that may be used in a variety ofelectronic applications. The dielectric materials of the presentinvention have low dielectric constant or low loss tangent, or both, canwithstand a wide range of temperatures, from both high temperatures ofapproximately +260° C. to low temperatures of approximately −200° C.,operate in a wide range of atmospheric conditions and pressures, e.g., ahigh atmosphere, low vacuum condition such as that found in theouter-space as well as conditions similar to those found at sea level,below sea level, or under-ground. These materials may further comprise amaterial that exhibits low moisture absorption, low x, y, z-axiscoefficient of thermal expansion (CTE), good dimensional stability inthe X and Y CTE, which may aid in the reliability of registration ofthrough holes and which will also be stable when exposed to ultraviolet(UV) light; has a low tensile modulus; and may be used in themanufacture of composite structures that can be used alone or incombination with other materials, thus making the present inventionsuitable for use in a variety of electronic applications. The low CTE ofthe subject dielectric material, may increase the reliability of throughhole connections and/or lessen any change in dielectric constant or losstangent of the material when holes are plated through. In addition, thedielectric material, laminates made therefrom and assembliesincorporating such dielectric materials are resistant to attack byacidic aqueous media, basic aqueous media and/or organic media, makingit possible to subject such assemblies to a variety of processingconditions commonly used in printed circuit board manufacturing, suchas, for example, chemical etching to introduce circuitry thereto, aswell as permitting operation in harsh environments of such articlesincorporating the dielectric materials. The dielectric material of thepresent invention may also withstand manufacturing processes which mayallow drilling, milling, etching, and plating of interconnecting holesor high temperature exposure while processing withhot-air-solder-leveling (HASL) or lamination of components.

Other features and advantages of the present invention will becomeapparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating the preferred embodiments of the presentinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the present inventionwill become apparent to those skilled in the art from this detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION

As used herein and in the appended claims, the singular forms “a,” “an,”and “the”include plural references, unless the content clearly dictatesotherwise. Thus, for example, reference to “a dielectric material”includes a plurality of such dielectric materials and equivalentsthereof known to those skilled in the art, and reference to “thepre-sintered PTFE resin” is a reference to one or more such pre-sinteredPTFE resins and equivalents thereof known to those skilled in the art,and so forth. All publications, patent applications, patents, and otherreferences mentioned herein are incorporated by reference in theirentirety.

The present invention comprises methods and compositions for making andusing materials having at least one of a low dielectric constant and alow loss tangent. The materials of the present invention can be used inharsh environments, which may have temperatures of approximately +260°C. to approximately −200° C., or may have wide ranges of atmosphericconditions and pressures, such as under high atmospheric pressures tonear vacuum pressure, e.g., as those found at sea level, below sealevel, or under-ground as well as in outer-space. The materials of thepresent invention may be used in the manufacture of composite structuresthat can be used alone or in combination with other materials. As usedherein, the materials of the present invention are referred to as “lowdielectric materials”, but these materials are not limited to havingonly that characteristic, but may have one or all of the characteristicsdisclosed herein.

The low dielectric materials are useful as components of laminates,wherein the low dielectric material has one or more of its surfaces, ora portion of a surface, affixed or adjacent to another material, and arealso useful as a component or components of assemblies, includingcombinations of multiple laminate structures, or where multiple layersof low dielectric materials are used. Such laminates and assemblies areused in electronic devices and applications. Electronic devices andapplications include, but are not limited to, microstrip and striplinecircuits, millimeter wave applications, military radar systems, missileguidance systems, point to point digital radio antennas, antennas, andother elements of cellular and wireless technology including, but notlimited to, antennas for wireless communication systems, cellular basestations, LAN systems, automotive electronics, satellite TV receivers,microwave and RF components, radar systems, mobile communicationssystems, microwave test equipment, phase array antennas, ground basedand airborne radar systems, power backplates, high reliabilitymultilayer circuits, commercial airline collision avoidance systems,beam forming networks, airborne or other “friend or foe” identificationsystems, global positioning antennas and receivers, patch antennas,space saving circuitry, RF interconnects, and power amplifiers.

Technical requirements for materials used in high performance electronicdevices and applications include glass transition temperatures,dielectric constant and loss tangent, dimensional stability, lowcoefficient of thermal expansion, high thermal conductivity, lowz-direction expansion, have uncomplicated processing, and the ability towithstand complex and harsh chemical processing, allow plating ofconnecting holes, and withstand high temperatures used duringhot-air-solder-leveling (HASL) or lamination of components. Differentmaterials that make up the components of the laminates or assemblies arecombined to reach specific technical requirements for the specificapplication. One of the materials more crucial in reaching the desiredtechnical requirements is the dielectric material.

Many materials have been used in the electronics industry to providedielectric materials. For example, dielectric materials made from wovenor non-woven materials that are coated with resins are generally knownin the art. An example of such dielectric material is woven or non-wovenfiberglass, coated with polytetrafluoroethylene (PTFE) or filled PTFE.Such fiberglass is commonly used in high performance microwave typeprinted wired boards. The dielectric constant of such coated fibermaterials is reported to be 2.2 to 2.55 or higher if filled PTFE isused. Filled PTFE results from the addition of fillers such as ceramics,glass fibers, glass beads, carbon, graphite or molybdenum disulphide andother materials known to one skilled in the art to fill PTFE to altercertain properties of virgin PTFE.

The dielectric constant, also referred to as permittivity, Dk, Eps, orEr, is the property of a material that determines the relative speedthat an electrical signal will travel in that material. The relativedielectric constant ∈_(r) (represented as κ or K in some cases) isdefined as the ratio:∈_(r)=∈_(s)/∈₀where ∈_(s) is the static permittivity of the material in question, and∈₀ is the vacuum permittivity. This permittivity of free space isderived from Maxwell's equations by relating the electric fieldintensity E to the electric flux density D. In vacuum (free space), thepermittivity ∈ is just ∈₀, so the dielectric constant is unity. Signalspeed is roughly inversely proportional to the square root of thedielectric constant. A low dielectric constant will result in a highsignal propagation speed and a high dielectric constant will result in amuch slower signal propagation speed.

A related characteristic is the impedance of a laminate structure, suchas a printed circuit board. The impedance is determined by the thicknessof the laminate, which is the spacing between copper layers, and itsdielectric constant. Impedance control, and impedance matching ofcritical linked functional modules, is especially important in highspeed devices and applications. Thus, a feature of such laminates andassemblies is determined by the dielectric constant of the dielectricmaterial and the thickness and width of the metal conductor (e.g.,without limitation, copper, silver, gold, nickel, brass, and aluminum).

Related to dielectric constant (or permittivity) is dissipation factor,also known as, e.g., loss, loss tangent, LT, tan beta, and tan d. Thisis a measure of the percentage of the total transmitted power that willbe lost as power dissipates into the laminate material. Prior to thepresent invention, the PTFE-glass materials, PTFE materials, and PTFEmaterials filled with other materials such as, but not limited to,ceramics that have dielectric constants as low as 2.1, may havedissipation factor measurements or loss as low as 0.0009 and are some ofthe preferred materials for wide commercial uses for high speed, highfrequency applications including applications ranging in frequency fromabout 1 MHz to about 100 Ghz or higher.

Dielectric constants and dissipation factors are considered in makingand designing electronic components, for example, for high speed digitaland microwave applications. The low dielectric constant and/or low lossis important for materials handling high frequency, high volume digitaldata. These technical characteristics of dielectric constant ordissipation factor also relate to impedance control, which is also afactor considered when selecting materials for manufacturing high speed,high volume digital data transmission devices.

The dielectric materials of the present invention comprise materialsthat may have at least one of a low dielectric constant and a lowdissipation factor, and optionally, may withstand a wide range oftemperatures, from both high temperatures of about +260° C. to lowtemperatures of about −200° C., and may operate in a wide range ofatmospheric conditions and pressures, e.g., a high atmosphere, lowvacuum condition such as that found in the outer-space as well asconditions similar to those found at sea level or below sea level, aswell as exposure to UV light. The material may optionally exhibit lowmoisture absorption, low x, y, z-axis coefficient of thermal expansion(CTE) which may increase the reliability of through hole connections orhave less change in dielectric constant or loss tangent of the material,good dimensional stability in the X and Y CTE which may aid in thereliability of registration of through holes, and a low tensile modulus,or when combined with other composite materials, result in laminates orassemblies having improved impedance control. The dielectric material ofthe present invention may also withstand various manufacturing processesand may allow drilling, milling, etching, and/or plating ofinterconnecting holes or high temperature exposure while processing withhot-air-solder-leveling (HASL) or lamination of components.

In one aspect, the present invention provides a dielectric materialcomprising a dielectric constant of greater than about 1.0 and less thanat least about 1.9, less than about 1.8, less than about 1.7, less thanabout 1.6, less than about 1.5, less than about 1.4, less than about1.3, less than about 1.2, and less than about 1.1. The dielectricmaterial may have a dielectric constant within the ranges between about1.0 and the dielectric constant of PTFE. In one embodiment, thedielectric material of the present invention comprises a dissipationfactor or loss of less than about 0.0009. In another embodiment, thepresent invention provides a dielectric material comprising a dielectricconstant of greater than about 1.0 and less than at least about 1.9, anda loss of less than about 0.0009. In addition, the present inventionprovides PTFE dielectric materials for which the dielectric constant maybe controlled by manufacturing steps to be a specific dielectricconstant number or within a small range around a specific dielectricconstant number that is grater than about 1.0 and less than at leastabout 1.9.

An embodiment of the dielectric materials of the present inventioncomprises a PTFE material that may be manufactured to have a particularcharacteristic such as a specific dielectric constant and/or losstangent. Such dielectric materials may comprise microporous polymericmaterial, such as, without limitation, reduced density PTFE, andoptionally having a controlled void volume and density. Exemplaryembodiments of the dielectric materials of the present inventioninclude, without limitation, PTFE alone and PTFE in combination withother materials such as PTFE filled materials, PTFE film, PTFE coatedglass fibers or fabric. PTFE materials are known to those skilled in theart. Examples of conventional fillers for PTFE include, withoutlimitation, glass fibers, glass spheres, carbon, graphite, bronze,stainless steel, and molybdenum disulfide. Polymeric fillers may also beused.

In another aspect, the present invention provides methods of makingdielectric materials wherein the dielectric constant may be determinedby the effects of the pre-sintering process, the ratio of the sinteredresin to virgin resin, and the amount of pressure applied duringmolding. In various embodiments, methods of making dielectric materialscomprise: a) pre-sintering micron sized PTFE resin or filled PTFE resin;b) blending a predetermined ratio of pre-sintered PTFE resin orpre-sintered filled PTFE resin with un-sintered PTFE resin (alsoreferred to herein as virgin PTFE resin or filled virgin PTFE resin); c)molding mixture of pre-sintered/un-sintered PTFE resin or filled PTFEresin under controlled pressure to control the density of the materialand thereby forming a molded PTFE article; d) sintering the molded PTFEarticle; and e) optionally skiving the molded PTFE article.

Sintering is the consolidation and densification of moldedpolytetrafluoroethylene above its melting temperature. Typically, thesintering temperature for PTFE is within the range of 350° C. to 400° C.Before it is sintered, a PTFE preform, or un-sintered but molded part,is relatively soft and can be easily broken with a minimal appliedforce. After sintering, the molded part may become much harder, tougher,and more resilient.

In one embodiment, the present invention provides a reduced density PTFEwhich can be made by controlled pre-sintering of powders with a definedparticle size. For example, the PTFE of the present invention can bemade with PTFE particles of from about 10 microns to about 300 microns,with a D50max of about 100, or other known and available PTFE resins.Methods for making PTFE films are known and generally include placingthe PTFE resin particles and/or pre-sintered PTFE particles in aconventional or isostatic mold under pressure and further sintering thepreformed billet to form a product material which may then be skived toform a film. The molding may include preformed molding, isostaticmolding, or molding into a sheet or shape. The particles may or may notbe pre-sintered prior to molding.

Many factors may affect the physical properties of the resultingdielectric material, such as, without limitation, the particle size ofPTFE and/or any added fillers or other materials, pre-sinteringtemperature and time cycles, the ratio of pre-sintered PTFE toun-sintered PTFE resin, the molding pressure and final sinteringtemperature, and the inclusion or exclusion of fillers. Selection ofsuch manufacturing steps may be dependent on the needs of the finalarticle, composite or laminate.

For example, factors that affect the dielectric constant and thedissipation factor of the dielectric materials of the present inventionmay include the following. The dielectric constant and the dissipationfactor may increase or decrease by the amount of pre-sintering of thePTFE, by varying molding pressure, and the time and temperature of thesintering cycle. A method of the present invention comprises makingdielectric materials having a low dielectric constant that is greaterthan about 1.0 and less than at least about 1.9, wherein the PTFE resinis pre-sintered and then molded at a specific pressure and furthersintered for a period of time that is effective to yield the desireddielectric constant. Sintering or pre-sintering may be carried out inovens at about 350° C. to about 450° C., for about 10 minutes to about10 hours. In general, the more pre-sintering the PTFE undergoes and thehigher the ratio of pre-sintered to virgin PTFE, the lower thedielectric constant the final dielectric material may have.

In one embodiment, the dielectric constant of the desired product may becontrolled by changing the ratio of pre-sintered PTFE to un-sinteredPTFE. The un-sintered or virgin PTFE may be the same size range or adifferent size range as the pre-sintered PTFE. For example, theun-sintered or virgin PTFE may be from about 0.15 to about 350 microns,from about 20 to about 350 microns, from about 15 to about 30 microns,or may have a D50max of 5 microns, of 20 microns, of 50 microns or otherknown and available ranges. The ratio may be from about 99.9:1 to about0.1:99.9 pre-sintered PTFE:un-sintered PTFE, such as, about 50:50, about75:25, about 85:15, about 95:5, about 25:75, about 15:85, about 5:95,about 60:40, about 70:30, about 90:10, about 80:20, and all suitableratios in between. In general, the more pre-sintered PTFE in the ratio,the lower the dielectric constant the final dielectric material mayhave.

In another embodiment, the dielectric constant of the desired productmay be controlled by manipulating the mold pressure. The molding of thePTFE can be in any known molding means, including, but not limited to,billeting, molding, rolling, calendering, or isostatic molding whereinthe pressures may be from about 0.5 Kg/cm² to about 1000 Kg/cm², about0.5 Kg/cm² to about 100 Kg/cm², from about 50 Kg/cm² to about 500Kg/cm², from about 100 Kg/cm² to about 300 Kg/cm², from about 200 Kg/cm²to about 1000 Kg/cm², from about 25 Kg/cm² to about 200 Kg/cm², fromabout 500 Kg/cm² to about 1000 Kg/cm², or any suitable pressures inbetween. In general, the lower molding pressure, the lower the densityof the finished product, resulting in a lower the dielectric constantand loss tangent.

A factor that may determine the above factors is the requirements of thefinal product and the desired physical properties of the final product.For example, after molding, the dielectric material may be skived andmay have to have the physical integrity to be skived. Thus moldingpressure may have to be increased so that the material is sufficientlystrong, other factors would need to be adjusted to keep the dielectricconstant at the desired low number. It is the cumulative nature of theproperties and the interaction of factors that allows for theadjustments in the factors to reach the desired predetermined lowdielectric constant in the dielectric materials. For example, having ahigher ratio of virgin PTFE allows for greater physical integrity in thefinished dielectric material, but also a higher dielectric constant thana material made with a lower ratio of virgin PTFE.

The dielectric materials of the present invention, having a dielectricconstant of more than about 1.0 and less than about 1.9 and/or a loss ofless than 0.0009, may be used in composite assemblies. The dielectricmaterial may be used in an individual layer form, may be covered on oneor more surfaces by a polymeric film or membrane, such as, withoutlimitation, PFA (perfluoroalkoxy), ECTFE (ethylenechlorotrifluoroethylene), or FEP (fluoroethylene propylene), oradhesives, or may be used as part of multiple layers of dielectricmaterials of the same or different types of polymeric materials. Any ofthese dielectric material combinations may be used alone or incombination with one or more layers of conductive material, such as,without limitation, about 17 to about 70 μm rolled or electrodepositedcopper, copper foil, aluminum, brass, silver, gold, platinum, or otherconductive materials applied directly or indirectly on the dielectricmaterial, or other conductors to form assemblies such as circuit boards.

The thickness of the dielectric layer can vary widely, depending on theapplication. For example, a layer of the dielectric material may rangein thickness from about 0.00001 mm to about 100 mm or greater. Those ofskill in the art can readily determine suitable thickness of thedielectric material needed, depending on the end use intended for theresulting assembly.

The size of the void volume of the reduced density PTFE polymericdielectric material of the present invention can be controlled and mayvary, for example, according to the purpose of the application. The voidvolume of the dielectric material relates to the density of thepolymeric dielectric material. The void volume may correlate with Dk andDf properties in an inverse relationship. The void volume of thematerials of the present invention may range from about 5% to about 85%and may have a density ranging from about 0.6 to about 1.9 g/cm³. Thepreferred void volume and density may vary and can be controlled,depending on the end use intended for the dielectric material or theassembly made therefrom. For example, in various embodiments, when oneor more through-holes are drilled through or partially through anassembly, an open cell material with less void volume may be preferred.

An example of an assembly of the present invention comprises a layer ofthe dielectric material of the invention as described above, incombination with at least a second layer of material. For example alaminate may comprise a first layer of a conductive material in contactwith a layer of the dielectric material of the present invention havingat least one of a dielectric constant of more than about 1.0 and lessthan about 1.9 and a loss tangent of less than about 0.0009. Optionally,the dielectric layer may be in contact with one or more layers of aconductive material. Such a construct may comprise sandwiching thedielectric material between additional polymeric layers as well as theconductive layers. A laminate may also include other layers, such as alayer of material that is hydrophobic and impervious to other chemicalsused in manufacture of circuits. Such a hydrophobic layer may be placedbetween a dielectric layer and one or more of the conductive layers. Thelayers may be attached to one another by methods known to those skilledin the art, including, but not limited to, adhesive means or usingcofluoropolymers such as FEP or other polymers as an adhesive layer.Assemblies of the present invention also contemplate combinations ofmultiple layered structures. An example of an assembly is a printedcircuit board or a printed wire board.

Conductive layers contemplated for use in the practice of the presentinvention may be typically electrically conductive, althoughnon-conductive and/or semi-conductive materials may also be employed inthe practice of the present invention. Exemplary electrically conductivelayers include, without limitation, copper or an alloy thereof, nickelor an alloy thereof, nickel or nickel alloy plated copper, rolledcopper-invar-copper, aluminum, and combinations thereof. Such conductivelayers may cover the entire surface of the dielectric material of thepresent invention, or may also be narrow or defined conductive patternsas would be known to those in the art as lines, circuits, pathways,conductors, or vias.

For example, the first electrically conductive layer may be copper or analloy thereof. Similarly, the optional second electrically conductivelayer may be copper or an alloy thereof, a different conductivematerial, or a conductive layer comprising a non-conductive and/orsemi-conductive material.

An aspect of the present invention comprises an assembly wherein thefirst electrically conductive layer is capable of being converted intofrequency dependent circuitry. This may be accomplished by employingstandard techniques known in the art. An aspect of the present inventionis that an assembly can be subjected to conventional processingconditions for the preparation of circuitry thereon. Further, the secondelectrically conductive layer may be formed into a second frequencydependent circuit element, or it may be left intact to define a groundplane. This also can be prepared employing standard techniques known inthe art.

The dielectric materials contemplated for use in the practice of thepresent invention, including but not limited to reduced density PTFE,may be resistant to such exposure as acidic aqueous media, basic aqueousmedia, and/or organic media such as those typical used in themanufacture of etched printed circuits. Such materials may behydrophilic or hydrophobic. As readily recognized by those skilled inthe art, a variety of media are commonly employed for the preparationand processing of electronic circuitry. Such media include, for example,acidic aqueous media (which embraces aqueous solutions having a pH ofless than 7, to a pH of about 1 or less), basic aqueous media (whichembraces aqueous solutions having a pH of greater than 7, to about 13 orhigher), and organic media (which embraces non-polar organic solventssuch as hydrocarbons, aromatics, and the like, polar organic solventssuch as esters, halogenated hydrocarbons, and the like). The hydrophobicnature of the material can be made hydrophilic by exposure to sodiumbased chemicals such as FluoroEtch®, sodium ammonia, gases such ashelium, nitrogen, or hydrogen, or plasma-energized gasses.

The dielectric materials and assemblies taught herein may be used in anyelectronic device or component. Applications include, withoutlimitation, high frequency applications where low loss and controlleddielectric constant are required, such, but not limited to filters,couplers, low noise amplifiers, power dividers, and combiners, andapplications for low cost, light weight printed circuits are used, suchas printed circuit antennas for cellular infrastructure, automotiveradar and other microwave and RF applications. Electronic components ordevices include, without limitations, precision instrumentation,electronic components and computer applications of all types, andapplications including, but not limited to, circuitry components forelectronic applications, telephony, radiofrequencies, microwave or othersignal transmission in computers, telephones, electronic devices andcomponents used in engines, automobiles, space craft, marine craft,medical equipments, pipelines, and transmission and monitoring devices,including but not limited to, microstrip and stripline circuits,millimeter wave applications, military radar systems, missile guidancesystems, point to point digital radio antennas, antennas, and otherelements of cellular and wireless technology including, but not limitedto, antennas for wireless communication systems, cellular base stations,LAN systems, automotive electronics, satellite TV receivers, microwaveand RF components, radar systems, mobile communications systems,microwave test equipment, phase array antennas, ground based andairborne radar systems, power backplates, high reliability multilayercircuits, commercial airline collision avoidance systems, beam formingnetworks, airborne or other “friend or foe” identification systems,global positioning antennas and receivers, patch antennas, RFinterconnects, space saving circuitry, and power amplifiers. Thedielectric material of the present invention provides for electroniccomponents or devices having lower impedance than is currently availablebecause of the low dielectric constant or the low loss factor or both ofthe dielectric material. The dielectric material of the presentinvention is particularly suited to applications wherein closed cellpolymeric foams are not suited.

In another aspect, the present invention provides methods for theproduction of multiple circuits on a single large sheet of inventionassembly. This may be accomplished by creating a plurality of circuitsby a so-called “Step and Repeat” photo imaging process on the firstconductive layer of an invention assembly.

As readily recognized by those of skill in the art, assemblies can beapplied to any of a variety of substrates for use. For example, circuitsproduced employing assemblies can be mounted on support structures, suchas aluminum or composite materials intended as stiffeners, or the like,or can be combined with covers that act as protection from weather, forinstance.

In various embodiments, one of the characteristics of the dielectricmaterial of the present invention is the ability to withstand hightemperatures that may be experienced during the fabrication of circuitryusing processes like solder coating or hot-air-solder-leveling (HASL)which is used by those skilled in the art during circuit fabrication.

The dielectric material described in this invention may also have theability to allow interconnection of conductive layers by means ofdrilling through hole interconnects as readily recognized by thoseskilled in the art. Such interconnects can be made through a singlelayer of the dielectric material, or in combination with otherconductive or insulative layers. The method of creating theinterconnecting holes include, without limitation, drilling, plunging,boring, or by means of a laser or any other known method to attach toconnective layers on either side of the dielectric material or otherconductive layers, as readily recognized by those skilled in the art.After drilling through holes in an assembly, the hydrophobic nature ofthe dielectric material can be made hydrophilic by exposure to sodiumbased chemical such as FluoroEtch®, or gases such as helium, nitrogen,or hydrogen, or by means of gasses ignited with plasma energy in orderto plate the through holes with a conductor such as copper.

In accordance with yet another aspect of the present invention, thereare provided multilayer assemblies comprising a plurality of theabove-described assemblies of the invention. As readily recognized bythose of skill in the art, a “plurality” of assemblies refers to,without limitation, stacking 2 up to or greater than about 20 assembliesto produce complex interconnected circuitry, or any combination ofpluralities of the above-described assemblies and other conductive, nonconductive, insulative, or support type materials.

In one aspect, the present invention provides a PTFE material, whichcomprises at least one of a dielectric constant of more than about 1.0and less than about 1.9, and a loss tangent of less than about 0.0009.In one embodiment, the PTFE material may operate at a temperature fromabout −200° C. to about +260° C. In another embodiment, the PTFEmaterial may operate at a condition, such as, without limitation, anunder-water condition, an under-ground condition, an atmosphericcondition, an outer-space condition, or a condition wherein the lowdielectric constant PTFE material may be subject to ultraviolet lightexposure. In yet another embodiment, the PTFE material of the presentinvention may operate at a pressure from a near vacuum pressure to ahigh pressure, wherein the near vacuum pressure may be a pressure foundin an outer-space condition, and wherein the high pressure may be apressure found in an under-water or an under-ground condition. In stillanother embodiment, the PTFE material of the present invention mayoperate after at least one of a physical treatment and a chemicaltreatment, including, without limitation, a mechanical treatment,hole-drilling, a heat treatment, lamination, bonding, plating,hot-air-solder-leveling, an acidic aqueous media treatment, a basicaqueous media treatment, or an organic media treatment. Also providedare a PTFE material comprising a dielectric constant of more than about1.0 and less than about 1.9, a PTFE material comprising a loss tangentof less than about 0.0009, and a PTFE material, comprising a dielectricconstant of more than about 1.0 and less than about 1.9 and a losstangent of less than about 0.0009.

In another aspect, the present invention provides an article ofmanufacture, which comprises a PTFE material, wherein the PTFE materialcomprises at least one of a dielectric constant of more than about 1.0and less than about 1.9, and a loss tangent of less than about 0.0009.Examples of the article of manufacture include, without limitation, anassembly, a laminate, a combination of multiple laminate structures, anelectronic device, a circuit, a microstrip circuit, a multilayercircuit, a space saving circuitry, a stripline circuit, a millimeterwave system, a radar system, a ground based radar system, an airborneradar system, a missile guidance system, an antenna, a patch antenna, apoint to point digital radio antenna, a phase array antenna, a cellulardevice, a cellular base station, a wireless device, a mobilecommunications system, a LAN system, an automotive electronic article, asatellite TV receiver, a computer, a telephone, a microwave, a microwavetest equipment, a RF component, a RF interconnect, a power backplate, acommercial airline collision avoidance system, a beam forming network,an airborne identification system, a “friend or foe” identificationsystem, a global positioning antenna, a global positioning receiver, afilter, a coupler, a low noise amplifier, a power divider, a combiner, apower amplifier, an automobile, a space craft, a marine craft, a medicalequipment, a pipeline, a transmission device, or a monitoring device.

In yet another aspect, the present invention provides a PTFE material,which comprises at least one of a dielectric constant of more than about1.0 and less than about 1.9, and a loss tangent of less than about0.0009, wherein the PTFE material is obtained in accordance with amethod comprising: (1) sintering a plurality of micron sized PTFEresins, thereby obtaining a sintered PTFE material; (2) mixing aplurality of un-sintered micron sized PTFE resins with the sintered PTFEmaterial at a predetermined ratio, thereby obtaining a PTFE mixture; and(3) molding the PTFE mixture, thereby obtaining the PTFE material. Inone embodiment, the method may further comprise a step of skiving thePTFE material of step c), a step of sintering the PTFE material of stepc), or the combination thereof. In another embodiment, at least one ofthe plurality of micron sized PTFE resins and the plurality ofun-sintered micron sized PTFE resins may comprise a filler or a filledPTFE resin. In yet another embodiment, the PTFE material of the presentinvention may operate at a temperature from about −200° C. to about+260° C. In still another embodiment, the PTFE material of the presentinvention may operate at a condition, such as, without limitation, anunder-water condition, an under-ground condition, an atmosphericcondition, an outer-space condition, or a condition wherein the lowdielectric constant PTFE material may be subject to ultraviolet lightexposure. In addition, the PTFE material of the present invention mayoperate at a pressure from a near vacuum pressure to a high pressure,wherein the near vacuum pressure may be a pressure found in anouter-space condition, and wherein the high pressure may be a pressurefound in an under-water or an under-ground condition. The PTFE materialof the present invention may also operate after at least one of aphysical treatment and a chemical treatment, including, withoutlimitation, a mechanical treatment, hole-drilling, a heat treatment,lamination, bonding, plating, hot-air-solder-leveling, an acidic aqueousmedia treatment, a basic aqueous media treatment, or an organic mediatreatment.

Also provided is a method for making a PTFE material, comprising: (1)sintering a plurality of micron sized PTFE resins, thereby obtaining asintered PTFE material; (2) mixing a plurality of un-sintered micronsized PTFE resins with the sintered PTFE material at a predeterminedratio, thereby obtaining a PTFE mixture; and (3) molding the PTFEmixture, thereby obtaining the PTFE material. In one embodiment, themethod further comprises a step of skiving the PTFE material of step c),a step of sintering the PTFE material of step c), or the combinationthereof.

EXAMPLES Example 1 Making a Dielectric Material

PTFE with a D50 max 100 is sintered for 30 minutes in an oven at 375° C.The pre-sintered PTFE has in a 90:10 ratio with virgin PTFE and placedin a billet mold. The billet is molded at a pressure of 200 kg/cm². Themolded article is then sintered for 8 hours at 350° C. The sintered,molded articled is skived. The skived article will have a density of 1.4gm/cm³and the dielectric constant is 1.5±0.2. The article formed a flatfilm-like article that skived well and maintained its physicalintegrity. The dielectric material could be used in circuit boards,insulators, radar, microwave, RF interconnects components or otherapplications.

Example 2 Method for Making a Dielectric Material

200 micron PTFE with a filler of 5 percent glass fiber, with a D50 maxof 50 is pre-sintered for 90 minutes in an oven at 390° C. Thepre-sintered filled PTFE has a ratio of 85:15to virgin PTFE and placedinto a flat mold at a thickness of 0.050″. The mold is pressed at apressure of 300 kg/cm². The molded article is sintered for 3 hours at350° C. The finished article is tested and has a dielectric constant of1.85+/−0.15 and a density of 1.75 gm/cm³. The dielectric material couldbe used in circuit boards, insulators, RF interconnects, radarmicrowave, components or other applications.

Example 3 Molding a Shaped Dielectric Material

170 micron PTFE with a filler of 15 percent ceramic, with a D50 max of20 is pre-sintered at 400° C. in an oven for 60 minutes. Thepre-sintered filled PTFE has a ratio of 45:55 to virgin PTFE. Thematerial is pressed in a cone-shaped mold at a pressure of 900 kg/cm².The molded part is sintered for 10 hours at a temperature of 365° C. Themolded part is tested and has a dielectric constant of 1.7+/−0.2 and adensity of 1.65 gm/cm³. The dielectric material could be used inantennas, RF interconnects, or radar systems.

Whereas this invention has been described in detail with particularreference to preferred embodiments, it is understood that variations andmodifications can be effected within the spirit and scope of theinvention, as described herein before and as defined in the appendedclaims. The corresponding structures, materials, acts, and equivalentsof all means plus function elements, if any, in the claims below areintended to include any structure, material, or acts for performing thefunctions in combination with other claimed elements as specificallyclaimed.

1. A polytetrafluoroethylene (PTFE) material, comprising a mixture of atleast sintered PTFE resin, which is sintered prior to mixing, andun-sintered PTFE resin, wherein the material comprises at least one of adielectric constant of more than about 1.0 and less than about 1.9, anda loss tangent of less than about 0.0009.
 2. The PTFE material of claim1, wherein the PTFE material operates at a temperature from about −200°C. to about +260° C.
 3. The PTFE material of claim 1, wherein the PTFEmaterial operates at a condition, wherein the condition is anunder-water condition, an under-ground condition, an atmosphericcondition, an outer-space condition, or a condition wherein the lowdielectric constant PTFE material is subject to ultraviolet lightexposure.
 4. The PTFE material of claim 1, wherein the PTFE materialoperates at a pressure from a near vacuum pressure to a high pressure,wherein the near vacuum pressure is a pressure found in an outer-spacecondition, and wherein the high pressure is a pressure found in anunder-water or an under-ground condition.
 5. The PTFE material of claim1, wherein the PTFE material operates after at least one of a physicaltreatment and a chemical treatment.
 6. The PTFE material of claim 5,wherein one of the at least one of a physical treatment and a chemicaltreatment is a mechanical treatment, hole-drilling, a heat treatment,lamination, bonding, plating, hot-air-solder-leveling, an acidic aqueousmedia treatment, a basic aqueous media treatment, or an organic mediatreatment.
 7. The PTFE material of claim 1, wherein the PTFE material iscomprised in an assembly, a laminate, a combination of multiple laminatestructures, an electronic device, a circuit, a microstrip circuit, amultilayer circuit, a space saving circuitry, a stripline circuit, amillimeter wave system, a radar system, a ground based radar system, anairborne radar system, a missile guidance system, an antenna, a patchantenna, a point to point digital radio antenna, a phase array antenna,a cellular device, a cellular base station, a wireless device, a mobilecommunications system, a LAN system, an automotive electronic article, asatellite TV receiver, a computer, a telephone, a microwave, a microwavetest equipment, a RF component, a RF interconnect, a power backplate, acommercial airline collision avoidance system, a beam forming network,an airborne identification system, a “friend or foe” identificationsystem, a global positioning antenna, a global positioning receiver, afilter, a coupler, a low noise amplifier, a power divider, a combiner, apower amplifier, an automobile, a space craft, a marine craft, a medicalequipment, a pipeline, a transmission device, or a monitoring device. 8.A PTFE material, comprising a mixture of at least sintered PTFE resinand un-sintered PTFE resin having at least one of a dielectric constantof more than about 1.0 and less than about 1.9, and a loss tangent ofless than about 0.0009, wherein the PTFE material is obtained inaccordance with a method comprising, a) sintering a plurality of micronsized PTFE resins, thereby obtaining a sintered PTFE resin; b) mixing aplurality of un-sintered micron sized PTFE resins with the sintered PTFEresin at a predetermined ratio, thereby obtaining a PTFE mixture; and c)molding the PTFE mixture, thereby obtaining the PTFE material.
 9. ThePTFE material of claim 8, further comprising a step of skiving the PTFEmaterial of step c), a step of sintering the PTFE material of step c),or the combination Thereof.
 10. The PTFE material of claim 8, wherein atleast one of the plurality of micron sized PTFE resins and the pluralityof un-sintered micron sized PTFE resins comprises a filler or a filledPTFE resin.
 11. The PTFE material of claim 8, wherein the PTFE materialoperates at a temperature from about −200° C. to about +260° C.
 12. ThePTFE material of claim 8, wherein the PTFE material operates at acondition, wherein the condition is an under-water condition, anunder-ground condition, an atmospheric condition, an outer-spacecondition, or a condition wherein the PTFE material is subject toultraviolet light exposure.
 13. The PTFE material of claim 8, whereinthe PTFE material operates at a pressure from a near vacuum pressure toa high pressure, wherein the near vacuum pressure is a pressure found inan outer-space condition, and wherein the high pressure is a pressurefound in an under-water or an under-ground condition.
 14. The PTFEmaterial of claim 8, wherein the PTFE material operates after at leastone of a physical treatment and a chemical treatment.
 15. The PTFEmaterial of claim 7, wherein the PTFE material is comprised in anassembly, a laminate, a combination of multiple laminate structures, anelectronic device, a circuit, a microstrip circuit, a multilayercircuit, a space saving circuitry, a stripline circuit, a millimeterwave system, a radar system, a ground based radar system, an airborneradar system, a missile guidance system, an antenna, a patch antenna, apoint to point digital radio antenna, a phase array antenna, a cellulardevice, a cellular base station, a wireless device, a mobilecommunications system, a LAN system, an automotive electronic article, asatellite TV receiver, a computer, a telephone, a microwave, a microwavetest equipment, a RF component, a RF interconnect, a power backplate, acommercial airline collision avoidance system, a beam forming network,an airborne identification system, a “friend or foe” identificationsystem, a global positioning antenna, a global positioning receiver, afilter, a coupler, a low noise amplifier, a power divider, a combiner, apower amplifier, an automobile, a space craft, a marine craft, a medicalequipment, a pipeline, a transmission device, or a monitoring device.